1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a polarized light emitting light guide plate, a method of manufacturing the same, and an illuminator for a flat panel display device using the polarized light emitting light guide plate, and more particularly, to a polarized light emitting plate which can emit light with a predetermined polarized component, a method of manufacturing the same, and an illuminator for a flat panel display device using the polarized light emitting light guide plate.
2. Description of the Related Art
Flat panel displays are classified into emissive displays, which form images by emitting light themselves, and non-emissive displays, which form images by receiving light from an external source. For example, a liquid crystal display is a non-emissive flat panel display device. A non-emissive flat panel display device such as a liquid crystal display requires an additional illumination system such as a backlight unit. However, conventional liquid crystal displays only use about 5% of the light emitted from a light source. Such low light use efficiency is mainly due to light absorption in polarization plates and color filters of the liquid crystal display. Specifically, since absorptive polarization plates, which are disposed on both sides of the liquid crystal display, absorb about 50% of unpolarized incident light, the absorptive polarization plates are the greatest cause of the low light use efficiency of the liquid crystal display.
In order to solve this problem, a backlight unit that emits light having the same polarization as a rear surface polarization plate or a polarizer attached on a rear surface of a liquid crystal display has been suggested. For example, an edge type backlight unit having a light source disposed at a lateral side of a light guide plate may include a multi-layered, reflective polarization film, such as a dual brightness enhancement film (DBEF), disposed onto an upper surface of the light guide plate to increase the light using efficiency of the liquid crystal display. However, this additional reflective polarization film is expensive, and the increase in the light use efficiency resulting from its usage is limited due to the lack of a polarization conversion member. Therefore, research is being conducted to create a polarized light emitting light guide plate that polarizes and converts light by itself.
FIG. 1 is a schematic view of a polarized light emitting light guide plate disclosed in U.S. Patent Publication No. 2003/0058386 A1. Referring to FIG. 1, the conventional polarized light emitting light guide plate 10 includes an anisotropic light separation layer 13 having an embossing surface 14 formed on an isotropic light guide plate 11. Also, an isotropic addition layer 15 having a flat surface is formed on the anisotropic light separation layer 13. The anisotropic light separation layer 13 is formed, for example, by uniaxially stretching a polymer sheet such as a poly ethylene terephthalate (PET) sheet or a poly ethylene naphthalate (PEN) sheet, thus having different refractive indices with respect to s-polarized light and p-polarized light, and hot embossing the same. In the polarized light emitting light guide plate 10 illustrated in FIG. 1, the refractive index of the anisotropic light separation layer 13 is higher with respect to s-polarized light than with respect to p-polarized light. Also, the refractive index of the isotropic light guide plate 11 is between the two refractive indices of the anisotropic light separation layer 13, and the refractive index of the isotropic addition layer 15 is equal to the refractive index of the anisotropic light separation layer 13 with respect to p-polarized light.
In the polarized light emitting light guide plate 10, light bs1+bp1 is incident on an upper surface of the light guide plate 11 at a smaller angle than a critical angle with respect to p-polarized light among light b traveling inside the light guide plate 11. The light bs1+bp1 is separated into an s-polarized component bs1 and a p-polarized component bp1 in the light separation layer 13. The s-polarized component bs1 passes through the isotropic addition layer 15 and is emitted to the outside, and the p-polarized component bp1 is totally reflected at an upper surface of the isotropic addition layer 15. Also, an s-polarized component bs2 of light bs2+bp2 that is incident on the upper surface of the light guide plate 11 at a greater angle than the critical angle with respect to p-polarized light is not totally reflected but is output to the outside through the light separation layer 13 and the isotropic addition layer 15. A p-polarized component bp2 is totally reflected at the upper surface of the light guide plate 11. Accordingly, the light emitted through the polarized light emitting light guide plate 10 is s-polarized.
However, when manufacturing the conventional polarized light emitting light guide plate 10, uniform uniaxial stretching of the anisotropic light separation layer 13, especially for larger size, is difficult. Also, in order to attach the light separation layer 13 to the upper surface of the light guide plate 11, a UV-curable adhesive coating layer 12 is needed, and the additional coating layer 15 needs to be formed using a UV-curable material. Thus, the manufacturing process of the conventional polarized light emitting light guide plate 10 is complicated.
FIG. 2 illustrates a method of manufacturing another conventional polarized light emitting light guide plate 20. Referring to FIG. 2, the conventional polarized light emitting light guide plate 20 is manufactured by attaching a liquid crystal polymer 23 to an isotropic light guide plate 21 in which a fine polarization separation pattern 22 is formed. However, since the liquid crystal polymer 23, which is cured on the transparent substrate 24, is used, a predetermined amount of light is lost due to the existence of the transparent substrate 24. Also, since a hot pressing process is conducted in order to attach the already cured liquid crystal polymer 23 to the light guide plate 21, the anisotropy of the liquid crystal polymer may be adversely affected due to high temperature and high pressure, and the polarization separation pattern 22 on the light guide plate 21 may be damaged.